The exact month or day or even the year of Jesus' birth cannot be exactly ascertained. Due to a mistaken calculation based on the Roman Calendar by Dionysius Exiguus in 525, it was long held that Jesus was born in the year 1 BC
making the following year, AD 1, the first throughout which he was
alive.

The Gospels are problematic, because they offer two accounts that chronologists find incompatible. Matthew states that Jesus was born while Herod the Great was still alive and that Herod ordered the slaughter of infants two years old and younger (Matt. 2:16), and based on the date of Herod's death in 4 BC (contra Dionysius Exiguus), many chronologists conclude that the year 6 BC is the most likely year of Jesus' birth. Consequently, Jesus would have been about four to six years old in the year AD 1.

On the other hand, Luke's account places Jesus' birth during a census conducted under the governorship of Quirinius, who, according to Josephus, conducted a census in AD 6. In order to reconcile the two Gospel accounts, some have suggested that Josephus was mistaken or that Quirinius had a separate period of rule under Herod. In any case, the actual date of his birth remains historically unverifiable.

In recent years, East Asian historians have attempted to match the birth of Jesus with special events in their history. They found that, according to the oldest record of the Comet Halley during the Han Dynasty, "The comet heads east with its tail pointing west at night, and was appearing in the sky for more than 70 days". in 6 BC. This has been suggested as an independent record of the "Star" described in Matthew 2. If accepted, this suggestion would place the birthday of Jesus in summer rather than winter.

In the 6th century, Dionysius Exiguus proposed to make the birth of Jesus the basis of the calendar but he miscalculated the death of Herod. Years reckoned in this way are labelled "A.D.", which stands for Anno Domini, meaning "in the year of the Lord" in Latin. Since many non-Christians have come to use this calendar, an alternative notation "C.E." is sometimes used. It is presently uncertain what the original meaning of this abbreviation was, although today it is taken to mean either the Common Era or the Christian Era: many references cite both.

Based on inferences from Gospel accounts, Jesus was executed by crucifixion on a Friday, and on the 14th day of the Jewish month of Nisan under the administration of Pontius Pilate. Pontius Pilate held his position from 26-36 and the only years in which Nisan 14 fell on a Friday are 27, 33, and 36 and possibly in 30 depending on when the new moon would have been visible in Jerusalem. Scholars have defended all of the dates.

This understanding of the Gospels is difficult to reconcile with the tradition that holds the Last Supper took place on the first night of Passover which is defined in the Torah to be the 14th of Nisan. Furthermore, at that time, the date of Passover was set by the court in Jerusalem based upon testimony of witnesses. It was not until after 500 that the calendar was changed to be based upon calculation. Therefore, it is not possible to state on which day of the week the 14 of Nisan occurred for any year before 500 without historical documents that attest to a particular day of the week.